1. Field of the Invention
The present invention relates to data communications using a contactless identification tag, and particularly to a contactless communication system that is preferably used to detect that the contactless identification tag attached to baggage (e.g., a package) and so on is improperly detached.
2. Description of the Related Art
In a conventional system, a tag including a shock sensor (refer to Japanese Unexamined Patent Application Publication No. 2002-150248) is attached to a piece of baggage so as to detect that a shock is added to the baggage, by detecting a voltage change caused when the shock sensor is disconnected by the shock beyond a certain amount (refer to Japanese Unexamined Patent Application Publication No. 2002-150249).
According to the invention as shown in Patent Document 2002-150249, although a shock can be usually detected, it is impossible to detect a shock when the tag is improperly detached because the shock sensor is not disconnected in such a case. Moreover, since the system provides no means to visually identify a tag to which the shock is added after detecting it, it requires complicated work to separate the tag to which the shock is added from other tags to which the shock is not added by detecting it again by means of the detection system.
According to the invention as shown in Patent Document 2002-150248, the disconnection is detected by using the shock sensor as a part of an antenna. In this case, since a deviation in resonant frequencies blocks communications, it is impossible to discern whether the problem is a breakdown or a shock.
In consideration of the above-mentioned problems posed by the conventional art, the present invention aims to provide a contactless communication system, a contactless identification tag and a contactless identification tag control program to detect that the contactless identification tag attached to a given object is improperly detached.